Don't know if you can do this with the trees in the pots. Normally you would turn the pots up side down, wet the pots so you have a damp surface and add an acrylic fortifier to your mix. After the bottom and sides have setup you turn the pot over and finish the return on the inside of the pot. You only have to cover down to where the soil would start inside the pot. Since your pot is starting to deteriorate I don't now if it can stand up to the removing of the trees or any of the other process.

The only pot that has ever cracked was a concrete one that I did not make. It was under the deck on the back of the house and full of soil which froze and broke the planter. This planter had straight sides so it wasn't a matter of the sides slanting in. The directions I got with the planter from the manufacturer said not to leave it out over winter with just soil in it and if planted and sitting on the ground to break contact with the ground with a piece of wood. I have a couple with trees and I shove a piece of wood under them. Most of my hypertufa planters have trees or shrubs planted in them and they stay out all Winter. I use equal parts peat moss, sand and portland cement for most planters. By the way, even though that concrete planter cracked I really liked it so I still use it. I plant vines to cover the cracks. I have some nice size concrete urns from the same manufacturer. Their in Quakertown, Pa and they use to have a bargain area for concrete items with defects. I haven't been there in a while and I understand this place is only open on the weekends now.

I made hypertufa rings to set in mygarden. The edges of each ring stands about 8 inches above soil level. No bottoms, just the rings. My husband cut out the molds from a heavy black plastic tapered nursery plant pot by rolling it along the blade on his table saw. One ring from the top of the pot and the second ring from the bottom of the pot so there was about a 2-3" space between the two rings where I packed in the hypertufa mix. I laid the smaller ring inside the larger one on a piece of plywood covered with heavy plastic so nothing stuck. When cured for about 6 months outside in the weather, I set rings into soil and planted them with hostas and sedums. All thrived, I think because they could grow into well draining soil rather than into a container with a bottom. Even with drain holes, I think they still accumulate too much moisture in the winter for some hostas. One could make these planters square or round. Carve a design in rim and outside when dry to green stage, about two days after molding them.

A few years ago I was told, by the people at one of the transfer stations here on the Cape, that they would throw away much of the recycling materials. The volume of recycling material was far greater than the ability of the recycling plants to process it. They told me that they wanted to keep the public in the habit of recycling so that if they would be ready when there was places that could process it. I was disappointed to learn that I had been living with the false good feeling that my efforts to separate and deliver these items to their areas in the transfer station along with most everyone else resulted in a better world was largely a farse. Hopefully, there are many more plants to process this stuff. But watching 3 dump workers spend their day tending to the recycle area, people walking through no less than 8 container areas each week to separate their stuff, and dealing with criss-crossing cars in the area seemed like a wasted effort when I watched the container of milk jugs get emptied into the general refuse early in the morning before the place opened. That is when they explained to me that they could only find a home for some of the materials some of the time. It was very disappointing. I live in a different community now. I find it interesting that here we do not have to separate light cardboard from other trash. All cans, bottles, and plastic containers go into one container. I would love to know how they recycle that "co-mingled" material. I guess what I am saying is that there is not a lot of opportunities to find anyone eager to accept material to recycle because they have access to more of it than they know what to do with. The best bet for recycling plant pots is to get them to someone who can use them as plant pots. But, the expense of washing process, storage, and handling might outweigh their value.